<template>
  <div class="uploadexcel-container">
    <p style="padding: 5px 10px; background-color: #e5e5e5;margin: 0 auto;text-align: center;">
      实现方式是原作者的代码修改得来
    </p>
    <input type="file" accept=".xlsx, .xls" ref="file-upload" @change="handleChange" style="display: none;"/>
    <div class="upload-container" @drop="handleDrop" @dragover="handleDragover" @dragenter="handleDragover">
      <span style="color: #909399;">Drop excel file here or</span>
      <el-button :loading="loding" type="primary" size="small" @click="handleUpload">Browse</el-button>
    </div>
    <el-table :data="tableDatas" border highlight-current-row>
      <el-table-column v-for="(item, index) in Header" :key="index" :label="item" :prop="item"></el-table-column>
    </el-table>
  </div>
</template>

<script>
import XLSX from 'xlsx'
export default {
  data() {
    return {
      tableDatas: [],
      Header: [],
      loding: false
    }
  },
  mounted() {
    const elMain = document.querySelector('.el-main')
    const uploadExcelContainer = document.querySelector('.uploadexcel-container')
    uploadExcelContainer.style.minHeight = elMain.offsetHeight - 20 + 'px'
  },
  methods: {
    generateData({ header, results }) {
      this.Header = header
      this.tableDatas = results
    },
    handleDrop(e) {
      e.stopPropagation()
      e.preventDefault()
      if (this.loading) return
      const files = e.dataTransfer.files
      if (files.length !== 1) {
        this.$message.error('Only support uploading one file!')
        return
      }
      const rawFile = files[0]

      if (!this.isExcel(rawFile)) {
        this.$message.error('Only supports upload .xlsx, .xls, .csv suffix files')
        return false
      }
      this.upload(rawFile)
      e.stopPropagation()
      e.preventDefault()
    },
    handleDragover(e) {
      e.stopPropagation()
      e.preventDefault()
      e.dataTransfer.dropEffect = 'copy'
    },
    handleUpload() {
      this.$refs['file-upload'].click()
    },
    handleChange(e) {
      const files = e.target.files
      const rawFile = files[0]
      if (!rawFile) return
      this.upload(rawFile)
    },
    upload(rawFile) {
      this.$refs['file-upload'].value = null

      if (!this.beforeUpload) {
        this.readerData(rawFile)
        return
      }
      const before = this.beforeUpload(rawFile)
      if (before) {
        this.readerData(rawFile)
      }
    },
    readerData(rawFile) {
      this.loading = true
      return new Promise((resolve, reject) => {
        const reader = new FileReader()
        reader.onload = e => {
          const data = e.target.result
          const workbook = XLSX.read(data, { type: 'array' })
          const firstSheetName = workbook.SheetNames[0]
          const worksheet = workbook.Sheets[firstSheetName]
          const header = this.getHeaderRow(worksheet)
          const results = XLSX.utils.sheet_to_json(worksheet)
          this.generateData({ header, results })
          this.loading = false
          resolve()
        }
        reader.readAsArrayBuffer(rawFile)
      })
    },
    getHeaderRow(sheet) {
      const headers = []
      const range = XLSX.utils.decode_range(sheet['!ref'])
      let C
      const R = range.s.r
      /* start in the first row */
      for (C = range.s.c; C <= range.e.c; ++C) { /* walk every column in the range */
        const cell = sheet[XLSX.utils.encode_cell({ c: C, r: R })]
        /* find the cell in the first row */
        let hdr = 'UNKNOWN ' + C // <-- replace with your desired default
        if (cell && cell.t) hdr = XLSX.utils.format_cell(cell)
        headers.push(hdr)
      }
      return headers
    },
    isExcel(file) {
      return /\.(xlsx|xls|csv)$/.test(file.name)
    }
  }
}
</script>

<style scoped>
  .upload-container {
    height: 150px;
    width: 40%;
    margin: 10px auto;
    border: 2px dotted #bbb;
    border-radius: 5px;
    display: flex;
    justify-content: center;
    align-items: center;
  }
  .uploadexcel-container {
    padding: 0 20px;
    border-top: 1px solid transparent;
    background-color: #fff;
  }
  .el-button{
    margin-left: 10px;
  }
</style>
